One of the hardest decisions to make in competitive bridge is which slam to bid when your side has most of the points. This hand came up at a team event so it was more beneficial to find the safest slam as opposed to the slam that would produce the best result.
South opened the bidding with one no trump. North responded two spades. This is a modern extension of transfers. If you are playing transfers over no trump, then two spades becomes a useless bid. It can then be used to show a strong, slam going hand, with a long minor suit. South is obliged to respond in his four card minor, if he has one, or two no trump, if he does not.
North is thrilled to hear that partner has a four card club suit and bids four no trump. This is Roman Key Card Blackwood, asking for key cards and, in this sequence, it also confirms clubs as the trump suit. "Key Cards" is defined as the four aces and the king of clubs. South's five spade response shows two key cards plus the queen of clubs. North now knows that a key card is missing and settles for the small slam in clubs.
West opens the nine of spades. Declarer calls for the king from dummy and decides how he wants to proceed. The only chance available to pick up the entire club suit without a loss is to find one hand with a singleton honor, and then guess which honor that is. If the king is singleton in either hand, declarer must play the ace and another club. If the jack is singleton, it must be with East, and declarer must lead the queen to both trap the king and smother the jack. In either case, this play is a long shot.
But knowing all this can be deceptive. Many players will just plunk down the ace because it is better than 75% that the outstanding clubs will break two-one. On this hand that equates to down one. Had you been playing a grand slam with these cards it would be worth your while to play for a singleton honor, since that is the only holding that allows you to make your contract.
In the small slam, it is the perfect time for a safety play. Win the first trick in the South hand and lead a small club toward the dummy simply covering any card that West plays. If West shows out, win the ace and return a club toward the queen. In any event, you will only lose one club trick no matter how they divide.
The moral of this hand is to look for "safe" plays when your contract appears secure. If you have a cavalier attitude you may soon find yourself being defeated in an ice cold contract.